The term "halogen compounds" refers to compounds containing chlorine, bromine, and the like. Numerous halogen compounds are useful flame retardant compounds for inclusion in polyolefin resin compositions. In general, the higher the halogen content in the compound, the better the flame retardant properties of the compound. For example, decabromodiphenyl oxide (DDO), also called decabromobiphenyl ether, which contains ten bromine atoms, has excellent flame retardant properties.
A problem with DDO and other high halogen content flame retardants is that they are not stable in the polyolefin resins into which they are incorporated. When articles are molded from resins containing such compounds, the fire retardant compounds migrate ("bloom") to the surface of the article and form a powder layer which can then rub off. The formation of such a powder layer is not only merely unsightly: it reflects an escape of the flame retardant compound from the molded article and a cosequential reduction in the flame retardancy characteristics. As a result, the art has taught away from using such high halogen containing compounds in polyolefin resins. For example, U.S. Pat. No. 4,548,964 to Yoshida and Mori, titled "Flame-Retardant Polyester Resin Composition," teaches as follows:
The other flame retarder which is used in combination with the flame retarder (C) must be HBBE (D) [or "hexabromobiphenyl ether"]. It is not desirable to use decabromobiphenyl ether which is analogous to HBBE but is different in bromine content. This is because, when a molded article containing decabromobiphenyl ether is exposed to elevated temperatures, the decabromobiphenyl ether blooms to the surface of the molded article and looks like a white powder. In contrast, HBBE barely escapes even at elevated temperatures and causes no change in the surface of the molded articles.
Accordingly, an object of the present invention is to provide polyolefin resins which include DDO or other high halogen content flame retardant compounds, in which the flame retardant compound is stabilized so it will not migrate to the surface of articles formed from the resin composition.